Based on the slender-body assumption, the 3-D flow is approximated to a set of unsteady 2-D ones. The effects of the all upstream sections (i.e. “memory effects”) are presented by integration. The whole problem can be devided into a wavemaking and an oscillating one according to the body boundary condition, the analytical expression of oscillating problem combined by wavemaking one is derived. As an example, the hydrodynamic derivatives of a slender-body of revolution are calculated.